Why Bridgestone's new run-flat tyres could be game-changers
Run-flat tyres have been derided for their poor ride quality, but new tech from Bridgestone aims to address that. We sample it first hand
Bridgestone revealed more details of its new DriveGuard tyre technology at an event in the UK recently.
The DriveGuard is a self-supporting run-flat tyre that can be fitted to conventional wheel rims and driven at speeds of up to 50mph for a maximum distance of 50 miles. The tyre can be fitted to any car equipped with a tyre pressure monitoring system (TPMS) and is compatible with standard rims.
When a conventional tyre deflates, the sidewalls collapse and fold, becoming trapped between the wheel rim and the road. If the car carries on driving, a combination of the pressure exerted by the rim on the trapped carcass and the heat generated in the folded sidewall leads to the rapid destruction of the tyre.
Self-supporting run-flat tyres have thick sidewall inserts with enough strength to keep the rim suspended above the ground when the tyre is deflated. The downside is that the thicker section and increased rigidity of the sidewalls impairs ride quality compared with conventional tyres.
The DriveGuard is constructed using Bridgestone’s proprietary Nano Pro-Tech technology, which evens out the distribution of sulphur bonds between the carbon molecules in the compound. This chemistry reduces internal friction within the material and inhibits heat generation in the sidewalls. Heat build-up is further reduced as the tyre rolls along by a cooling fin design moulded into the sidewall.
The combination of these factors allows a thinner sidewall construction and this, combined with a new crown structure to better absorb bumps and lumps in the road surface, is claimed to deliver comfort levels comparable with those of standard tyres.
An advanced polyester carcass body ply design reduces heat generation and helps the tyre to hold its shape when deflated. The thinner sidewalls also help to keep weight down, an important factor when manufacturers are struggling to remove every gram of weight to save fuel and reduce CO2 emissions.
We haven’t had the chance to test the claims of improved ride quality from behind the wheel yet, but we did have a demonstration ride in the passenger seat of a Vauxhall Astra with a front tyre completely deflated. The car steered around a low-speed handling course without drama and rode well enough that the flat wasn’t immediately obvious without TPMS.
The Astra was fitted with the more accurate type of TPMS, which displays an absolute tyre pressure in the instrument display via wireless pressure sensors in the wheels. The test runs started with zero pressure showing for the deflated tyre, but after a couple of laps the heat generated in the tyre was enough to expand residual air and raise the pressure to 1psi. Tyres generate some heat whether deflated or not, and this suggests the integrity of the tyre remained intact, allowing it to reinflate slightly, whereas a conventional tyre would have been damaged beyond repair.
Bridgestone says a punctured DriveGuard can be repaired by authorised dealers, as long as the sidewall or the structure of the tyre hasn’t been compromised in any way. A tyre inflation system can be used, but Bridgestone warns against reinflating a tyre that has been run flat without expert inspection first.
The DriveGuard scores well under the EU tyre labelling scheme with ‘A’ for wet performance and ‘C’ for rolling resistance. According to a Bridgestone technician, achieving high scores in all of these areas with a run-flat tyre is a challenge because of the stiffer sidewalls.
The DriveGuard is on sale in the UK now in 19 summer and 11 winter sizes, ranging from 185/65 R15 to 245/40 R18. The cost is 10-12% higher than that of a Bridgestone Turanza, or about £365, fitted, for a set of four in 225/45 R17 size.